What the achievement asks
Defeat Overseer Korgus in Tol Dagor on Heroic difficulty or higher. Ten points, both factions.
Tol Dagor is the island prison off Boralus, bought and run by the Ashvane Company, and the dungeon is a break-in rather than a break-out.
The four encounters
| Order | Encounter |
|---|---|
| 1 | The Sand Queen |
| 2 | Jes Howlis |
| 3 | Knight Captain Valyri |
| 4 | Overseer Korgus |
The prison climbs upwards rather than running flat, so the route is more vertical than most and easy to lose your bearings in. The bosses come in order regardless.
Heroic or higher, but on one character
Blizzard's wording is "on Heroic difficulty or higher", so a Mythic or Mythic Plus run earns it just as well. There is no need to queue for Heroic specifically.
The eight Heroic dungeon achievements are not account-wide. Four on your main and four on an alt leaves you with nothing. They all have to be earned by the same character.
Once one character holds all eight, the Battle for Azeroth Dungeon Hero achievement they feed into is account-wide, so the grind only has to happen once.